Jetting device and a method of jetting device

ABSTRACT

A jetting device and a method of jetting droplets of viscous medium onto a substrate. The jetting device includes a jetting outlet through which the droplets are jetted. The jetting device further includes a wall located at the jetting outlet, downstream of the jetting outlet seen in the jetting direction. The wall is provided with an orifice through which jetted droplets are permitted to pass through. A gaseous flow is provided within the space past the jetting outlet such that an adverse effect on the performance of the jetting device is prevented, the adverse effect resulting from the accumulation of viscous medium residue at the jetting outlet.

[0001] This application is the national phase under 35 U.S.C. § 371 ofPCT International Application No. PCT/SE02/00807 which has anInternational filing date of Apr. 25, 2002, which designated the UnitedStates of America, the entirety of which is hereby incorporated byreference.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention generally relates to the field of jettingdroplets of a viscous medium onto a substrate. More specifically, theinvention relates to a method of improving the performance of a jettingdevice, and a device for jetting droplets of viscous medium onto asubstrate.

BACKGROUND OF THE INVENTION

[0003] Devices of the above mentioned kind are known and are primarilyintended to be used for jetting droplets of viscous medium, e.g. solderpaste or glue, onto a substrate, e.g. an electronic circuit board, priorto mounting of components thereon. An example of such a jetting deviceis disclosed in WO 99/64167. The jetting device comprises an ejectchamber for containing a small volume of said medium prior to thejetting thereof, an eject nozzle communicating with the eject chamber,eject means for jetting said medium from the eject chamber through theeject nozzle, and supply means for feeding said medium into the ejectchamber. In WO 00/62587 there is disclosed an assembly comprising such ajetting device.

[0004] The production speed is an essential factor in the manufacturingof electronic circuit boards. This has lead to a desire of increasingthe speed at which a substrate is provided with viscous medium, a way ofeffecting this is to perform the actual jetting “on the fly”, i.e.without stopping for each location on the substrate where viscous mediumis to be deposited. A further way to improve the manufacturing speed ofelectronic circuit boards is to eliminate or reduce the need foroperator interventions.

[0005] Both of these measures require good and reliable performance ofthe device used in the process, as well as a high degree of accuracy anda maintained high level of reproducibility during an extended period oftime. The high quality requirements of the electronic industry and thedetrimental consequences of errors appearing in circuit boards evenfurther emphasise these requirements.

SUMMARY OF THE INVENTION

[0006] Thus, an object of the present invention is to improve theperformance of a device for jetting droplets of viscous medium onto asubstrate.

[0007] This and other objects are achieved according to the presentinvention by providing a method of jetting droplets of viscous mediumonto a substrate and a device for jetting droplets of viscous mediumonto a substrate.

[0008] According to a first aspect of the present invention, there isprovided a method for jetting droplets of viscous medium onto asubstrate, said jetting device comprising a jetting outlet through whichsaid droplets are jetted, comprising the steps of providing a gaseousflow past the jetting outlet such that an adverse effect on theperformance of the jetting device that may result from accumulation ofviscous medium residue at the jetting outlet is prevented, providing awall at the jetting outlet, said wall being located downstream of thejetting outlet seen in the jetting direction, and providing an orificein said wall for permitting the jetted droplets to pass through theorifice, the orifice and the jetting outlet being aligned in the jettingdirection.

[0009] According to a second aspect of the present invention, there isprovided a method of jetting droplets of viscous medium onto asubstrate, said jetting device comprising a jetting outlet through whichsaid droplets are jetted, comprising the step of providing a gaseousflow past the jetting outlet such that an adverse effect on theperformance of the jetting device that may result from accumulation ofviscous medium residue at the jetting outlet is prevented, wherein thegaseous flow at the jetting outlet is directed along a flow path thatintersects the jetting path of the jetted droplets.

[0010] According to a third aspect of the present invention, there isprovided a method of jetting droplets of viscous medium onto asubstrate, said jetting device comprising a jetting outlet through whichsaid droplets are jetted, comprising the step of providing an air flowpast the jetting outlet such that an adverse effect on the performanceof the jetting device that may result from accumulation of viscousmedium residue at the jetting outlet is prevented, wherein said air flowis provided through suction during, between and following the jetting ofindividual droplets.

[0011] According to a fourth aspect of the present invention, there isprovided a device for jetting droplets of viscous medium onto asubstrate, said device comprising a nozzle having a jetting outletthrough which said droplets are jetted, a flow generator for producing agaseous flow, a flow guide for providing a flow path for said gaseousflow past the jetting outlet, such that an adverse effect on theperformance of the jetting device that may result from accumulation ofviscous medium residue at the jetting outlet is prevented, wherein saidflow guide comprises a wall located at the jetting outlet, said wallbeing located downstream of the jetting outlet seen in the jettingdirection, said wall and said nozzle defining a first spacethere-between, and a first orifice provided in said wall, said firstorifice and the jetting outlet being aligned along the path of thejetted droplets, said first orifice being designed to permit jetteddroplets to pass through said first orifice essentially unaffected,wherein said flow guide is arranged to provide said gaseous flow withinsaid first space along a flow path past the jetting outlet.

[0012] According to a fifth aspect of the present invention, there isprovided a device for jetting droplets of viscous medium onto asubstrate, said device comprising a nozzle having a jetting outletthrough which said droplets are jetted, a flow generator for producing agaseous flow, a flow guide for providing a flow path for said gaseousflow past the jetting outlet such that an adverse effect on theperformance of the jetting device that may result from accumulation ofviscous medium residue at the jetting outlet is prevented, said flowguide being arranged for providing said flow path in a direction thatintersects the jetting path of the jetted droplets.

[0013] For the purposes of this application, it is to be noted that theterm “viscous medium” should be interpreted as solder paste, flux,adhesive, conductive adhesive, or any other kind of medium used forfastening components on a substrate, conductive ink, resistive paste, orthe like; and that the term “substrate” should be interpreted as aprinted circuit board (PCB), a substrate for ball grid arrays (BGA),chip scale packages (CSP), quad flat packages (QFP), wafers, flip-chips,or the like.

[0014] It is also to be noted that the term “jetting” should beinterpreted as a non-contact dispensing process that utilizes a fluidjet to form and shoot droplets of a viscous medium from a jet nozzleonto a substrate, as compared to a contact dispensing process, such as“fluid wetting”, and that the term “gaseous flow” should be interpretedas a flow of air, compressed air, gas of any suitable type, such asnitrogen, or any other medium of a gaseous type.

[0015] Thus, the present invention relates to providing a gaseous flowat the jetting outlet of a jetting device for preventing an adverseeffect on the performance of the jetting device that may result fromaccumulation of viscous medium residue at the jetting outlet.

[0016] As described above, a jetting device generally comprises an ejectchamber communicating with a supply of viscous medium, and a nozzlecommunicating with the eject chamber. Prior to the jetting of a droplet,the eject chamber is supplied with viscous medium. Then, the volume ofthe eject chamber is rapidly reduced, causing a well-defined amount ofviscous medium to be forced with high velocity out of the orifice orexit hole of the nozzle and onto a substrate, thus forming a deposit ordot of viscous medium on the substrate. The jetted amount is hereinafterreferred to as a droplet or a jet.

[0017] During the actual jetting phase, the jetted viscous medium passesthrough the orifice of the nozzle and breaks off from the viscous mediumremaining in the eject chamber, thus forming a droplet or jet travellingtowards the substrate. During an instantaneous moment of the jettingphase, viscous medium passing the orifice is in contact with the orificesurrounding surfaces of the nozzle that are most adjacent to and facingthe substrate, i.e. surfaces not being in contact with viscous mediumbetween the jetting phases. The portion of the nozzle surrounding theorifice that is adjacent to and facing the substrate is hereinafterreferred to as the “jetting outlet”. Thus, the term “jetting outlet”does not include the portions of the nozzle facing the eject chamber,i.e. the portions being in contact with viscous medium between thejetting of droplets.

[0018] When jetting viscous medium, minute amounts of the medium tend toadhere or stick to the surfaces of the jetting outlet during the briefmoment of contact between the surfaces and the viscous medium. Thisoccurs due to the characteristics of the viscous medium. Since it is arequirement that the solder pastes or other viscous mediums adhere wellto a substrate, a so called tackifier is often used when preparing theviscous medium in order to achieve the desired adhesiveness. As aconsequence, viscous medium residue may remain attached or adhered tothe surfaces of the jetting outlet following the jetting of a droplet.It should be noted that viscous medium residue refers to the undesired,often minute amounts of viscous medium that breaks off from the dropletduring the jetting process. In this context, it refers to the amountsthat has become attached to some surface of the jetting device afterhaving been ejected out from the eject chamber.

[0019] According to the present invention, a gaseous flow is providedpast the jetting outlet, the magnitude and the velocity of the gaseousflow being sufficient for transporting viscous medium residue away fromthe area at the jetting outlet with the gaseous flow. Thus, the oftenminute quantities of viscous medium that following the jetting of adroplet remains attached to surfaces at the jetting outlet where noresidue is desired is loosened from said surface and carried away by thegaseous flow. Also, the gaseous flow provided past the jetting outletmay prevent certain quantities of viscous medium residue to attach tosaid surfaces in the first place.

[0020] As noted above, the presence of viscous medium residue, and thepossible accumulation thereof, at the jetting outlet may have an adverseeffect on the trajectory of the jetted droplets as they pass the jettingoutlet. Also, the viscous medium residue may interfere with the jetteddroplet so as to alter the volume of the droplet, e.g. a volume ofviscous medium residue situated at the jetting outlet may loosen fromthe surface and instead adhere to and be incorporated into the jetteddroplet. Furthermore, the residue may cause spattering of viscous mediumwhen a jetted droplet “collides” with the residue. Consequently, thepresence of viscous medium residue at the jetting outlet may causedeviations in the position, form or size of the resulting depositscompared to that intended. Also, there may be spatters of viscous mediumon the substrate, which spatters may form solder balls that move aroundfreely on the substrate during reflow and can, in turn, result inbridging, short circuits, and reduced reliability.

[0021] Thus, the accumulation or build-up of viscous medium residue hasan undesired influence on the jetting performance and, consequently, onthe overall performance of the jetting device. Particularly, theundesired presence of viscous medium residue at the jetting outlet willimpair the accuracy and the reproducibility of the device, especiallyover a period of time, due to the random build-up of undesired materialat the jetting outlet. It may also lead to inflicted undesired operatorinterventions, which brings about interruptions in the manufacturingprocess and thereby decreases the overall manufacturing speed.

[0022] Consequently, it is of great importance to prevent a negativeeffect on the jetting performance due to accumulation of viscous mediumresidue at the jetting outlet. In order to obtain a high manufacturingspeed, it is essential that this negative effect can be preventedwithout interruptions in the manufacturing process. In order to achievean effective jetting process it is desirable to provide the gaseous flowin a regulated way. For example, this can be achieved by providing thegaseous flow after the jetting of a series of droplets for removing andtransporting away viscous medium residue from the surfaces of thejetting outlet. According to one example, such a series constitutes apredetermined number of jetted droplets. According to another example,the series is made up of the droplets jetted during a predeterminedperiod of time. Preferably, the gaseous flow is provided according to apre-programmed scheme, taken into account said series of jetteddroplets, which scheme is controlled by some sort of control device.

[0023] Naturally, this can be combined, for example so that the gaseousflow is provided following a predetermined number of droplets, butwithin a predetermined maximum time period. This means that the gaseousflow is provided at specific intervals, unless the number of jetteddroplets within such a time interval exceeds a threshold value. If so,there is provided a gaseous flow and the time interval and number ofjetted droplets are reset. According to another preferred example, thegaseous flow is provided at each instant when there is no droplet jettedduring a given period of time. At these predetermined “pauses”, whichcan be the result of substrate exchange or any other reason, the gaseousflow is provided for removing viscous medium residue from the surfacesof the jetting outlet.

[0024] As an alternative to the predetermined or pre-programmedinstances for providing the gaseous flow at the jetting outlet, thegaseous flow can be provided “on demand”. Then, there is provided somesort of detector for detecting whether viscous medium residue hasaccumulated at the jetting outlet to such an extent that gaseous flowshould be provided. The detector could be any suitable detector knownwithin the art, such as a camera.

[0025] According to preferred embodiments of the invention, the gaseousflow is provided during the actual jetting of the droplets. Then, thegaseous flow is synchronised with the jetting periods, i.e. each time adroplet is jetted, there is provided a gaseous flow at the jettingoutlet. Preferably, this is achieved by providing a continuous gaseousflow throughout the entire jetting procedure. Alternatively, the gaseousflow is paused at the time when, or at a predetermined time periodafter, the jetting process is halted.

[0026] The provision of a gaseous flow during the jetting of dropletsprovides a number of advantages. First, any viscous medium residue thathas become attached to the jetting outlet surfaces following the jettingof a droplet is immediately transported from the vicinity of the jettingoutlet. Second, the gaseous flow can pick up and transport away from thejetting outlet minute quantities of viscous medium that has broken offfrom the droplet or jet and that would otherwise adhere to the surfacesof the jetting outlet as residue. Thus, the build-up or accumulation ofviscous medium residue at the jetting outlet to an adverse amount isprevented, whereby a high level of accuracy and reproducibility ismaintained during a jetting period.

[0027] A further advantage resulting from the provision of gaseous flowduring the actual jetting of a droplet is that satellites of viscousmedium can be picked-up and transported away from the vicinity of thejetting outlet. Said satellites being minute quantities of viscousmedium that undesirably breaks away from the droplet or jet of viscousmedium during jetting, thus forming a so called satellite. Satellites donormally have the same general direction as the droplet or jet, althoughwith an angular deviation that causes the satellites to hit thesubstrate spaced apart from the intended deposit. These satellites cancause the formation of solder balls that move around freely on thesubstrate during reflow and can, as stated above, result in bridging,short circuits, etc. Thus, the prevention of viscous medium satellitesimproves the result of the application of viscous medium onto thesubstrate and, hence, decreases the rejection rate of the completedsubstrates.

[0028] A still further advantage of providing gaseous flow at thejetting outlet during the jetting process is the possibility ofobtaining a stabilizing effect on the trajectory of the jetted droplet.For example, according to an embodiment of the invention, the gaseousflow is provided towards the jetting outlet in a direction opposite thatof the jetted droplet, i.e. axially directed along the jetting path.When reaching the jetting outlet, the flow is guided such that the flowaway from the jetting outlet is radially directed. Preferably, theaxially directed flow is essentially uniformly distributed, such that anessentially laminar flow is obtained that has a stabilizing effect onthe trajectory or flight path of the jetted droplets or jets.

[0029] According to the present invention, the gaseous flow is generatedthrough a flow generator. According to a preferred embodiment of thepresent invention, said flow generator is in the form of suctiongenerator, i.e. in the form of a vacuum ejector or any other suitabletype of suction generator. Said suction generator then being provideddownstream of the area surrounding the jetting outlet, as seen in thedirection of the gaseous flow.

[0030] An alternative way of producing the gaseous flow, according toanother preferred embodiment of the present invention, is to provideblow generator, preferably in the form of a source of pressurised gas orany other suitable type of blow generator. The blow generator then, ofcourse, being provided upstream of the area surrounding the jettingoutlet. One advantage of providing a blow generator, as compared to asuction generator, is that a pressure difference of more than oneatmosphere may be obtained.

[0031] According to a specific embodiment of the present invention acombination of a suction generator and a blow generator is provided forgenerating said gaseous flow. Then, the blow generator and suctiongenerator are suitably provided on opposite sides of the jetting outlet.

[0032] According to preferred embodiments of the present invention,there is provided a guide for guiding the gaseous flow to and from thevicinity of, or the portion surrounding, the jetting outlet.

[0033] According to preferred embodiments of the invention, the gaseousflow is directed and focused or concentrated past the jetting outletsuch that the flow velocity is increased to a level for optimising thetransport of viscous medium residue from the surfaces of the jettingoutlet, without adversely affecting the jetting process. This allows foran effective removal of viscous medium residue from the surfaces of thejetting outlet and decreases the possibility of viscous medium residueadhering to the jetting outlet surfaces, and thereby improves theaccuracy and maintains a high degree of reproducibility during thejetting process. This can be achieved by providing a narrowed flow pathpast the jetting outlet.

[0034] According to embodiments of the first aspect of the presentinvention, the jetting device is provided with a wall, the wall beingspaced apart from the jetting outlet and located downstream of thejetting outlet seen in the direction of the jetted droplets at thejetting outlet. Said wall may, as an example, constitute part of anozzle support, but can be provided without having any supportingfunction for the nozzle. Between the wall and the jetting outlet, thereis formed a space acting as a channel or guide for the gaseous flow atand past the jetting outlet.

[0035] According to a specific embodiment of the invention, the spaceformed between the jetting outlet and the wall acts as a channel for thegaseous flow. In this channel, one end of the space acts as an inlet,and the opposite end acts as an outlet for the gaseous flow, said endsbeing provided at opposite sides of the jetting outlet. Preferably, theend acting as an inlet communicates with a blow generator, and the endacting as an outlet communicates with a suction generator.Alternatively, only the blow generator or the suction generator,respectively, is provided. The communication between the space at thejetting outlet and said respective flow generator are preferablyprovided through channels, such that the flow generator can be providedat a distance from the jetting outlet.

[0036] Since said wall is located in the jetting path, the wall isprovided with an opening or orifice, concentric with the jetting outlet.The jetted droplets are thereby permitted to pass through the wall viathe orifice. According to a specific embodiment, the orifice of the wallalso functions as an inlet for the gaseous flow towards the jettingoutlet. An advantage of this embodiment is that a laminar flow can beprovided in the manner described above, said laminar flow having astabilizing effect on the trajectory of the jetted droplets or jets.Furthermore, in this embodiment, the jetted droplets will face a stronghead wind immediately following the jetting thereof. Droplets having ajetting trajectory that deviates angularly from that intended, willencounter a slight side wind. The effect of the side wind on a jetteddroplet will be dependent of the magnitude of the angular deviation. Asa consequence, the angular deviation can be enhanced to such an extentthat the jetted droplet will be collected by the wall.

[0037] Alternatively, one or more further orifices may be provided insaid wall, said further orifice(s) then acting as an inlet for thegaseous flow towards the jetting outlet.

[0038] According to a further embodiment of the invention, includingsaid wall and the orifice thereof through which the droplets are jetted,viscous medium satellites, produced during the jetting of droplets asdescribed above, are prevented from reaching the substrate. This isachieved by providing said orifice with such dimensions that, whereasthe jetted droplet is permitted to pass through the orifice, satelliteshaving a direction that deviates from that of the jetted droplets missthe orifice and are collected by the wall.

[0039] In the embodiment where the orifice of the wall constitutes aninlet for the gaseous flow towards the jetting outlet, any satellitesproduced will in the same manner as described above, due to theirangular deviation, encounter a side wind that enhances their angulardeviation such that they may be collected by the wall. Due to the lowervelocity and significantly smaller volume of the satellites, as comparedto the viscous medium droplets, the satellites will be much moresusceptible to the effects of the side wind.

[0040] As understood by the man skilled in the art, the gaseous flow maybe provided such that any viscous medium, e.g. jetted droplets orsatellites, collected by the wall is removed therefrom and transportedaway by the gaseous flow.

[0041] According to an example of the present invention, the focusing ofthe gaseous flow for optimizing or increasing the ability of the gaseousflow to transport viscous medium residue from the jetting outlet isobtained by providing the wall with a suitable design. According to oneembodiment, the wall is provided with an annular protrusion at andsurrounding the jetting outlet that decreases the area of the flow pathand thereby increases the flow velocity past the jetting outlet.However, as realized by the man skilled in the art, a vast number ofdifferent designs are possible to obtain the desired increase in flowvelocity and ability to transport viscous medium in accordance with thepresent invention.

[0042] Furthermore, the wall may be designed to minimize the surfacearea surrounding the orifice onto which viscous medium may possiblybecome attached. According to one exemplary embodiment, this is achievedby providing a bevelled surface around the orifice on the side of thewall facing the substrate. Then, the inward orifice surface facing theviscous medium droplet as the droplet passes the orifice may besignificantly reduced, which would reduce the risk of viscous mediumattaching to the wall surface and negatively affect the performance ofthe jetting device. Furthermore, providing a bevelled surface around theorifice will have the additional advantage of reducing the flowresistance into the orifice, thereby enabling a more efficient suctionand a reduced risk of turbulence.

[0043] According to an alternative embodiment, the wall is provided withat least one channel for providing a flow path for the gas towards thejetting outlet. Then, said at least one channel has an extension withinand along said wall, and is provided with at least one channel outlet atthe orifice of the wall. Preferably, each channel exit or outlet isarranged such that the gaseous flow is directed at the jetting outlet.In this embodiment, the gaseous flow is preferably provided by a blowerof some sort, preferably a source of pressurized gas in communicationwith the channel(s). This may of course be combined with a suctiondevice, as understood by the man skilled in the art.

[0044] According to a further exemplifying embodiment of the invention,the jetting outlet and the wall are comprised in a single integralstructure. Preferably, the integral structure is provided with a channelfor providing a narrow flow path that intersects the path of the jetteddroplets. Then, the term “jetting outlet” refers to the portion of theintegral structure that faces the “upper” side of the flow path, i.e.the side of the flow path facing the eject chamber. As understood by theman skilled in the art, the wall can be of any suitable form or shapewith an orifice, concentric with the jetting outlet, as described above.

[0045] According to preferred embodiments of the second aspect of theinvention the gaseous flow is provided in a direction intersecting thepath of the jetted droplets. According to a specific embodiment, thegaseous flow is directed essentially perpendicularly to the path of thejetted droplets. Preferably, the gaseous flow is provided past andsweeping along the surfaces of the jetting outlet.

[0046] It should be noted that according to embodiments of the secondaspect of the present invention, for embodiments that utilize both asuction generator and a blow generator located on opposite sides of thejetting outlet, the provision of a wall of the type described inrelation to the first aspect of the invention is not essential. Thus,there could be provided an open space between the jetting outlet and thesubstrate without omitting the possibility to provide a gaseous flowpast the jetting outlet of sufficient amount and velocity to prevent anadverse effect on the performance of the jetting device from viscousmedium residue at the jetting outlet.

[0047] According to preferred embodiments of the invention, there isprovided a filter for collecting viscous medium transported from thevicinity of the jetting outlet by the gaseous flow. The filter is alsoprovided for preventing viscous medium from ending up in the suctiongenerator, for the embodiments where such is provided.

[0048] Furthermore, there may be provided a collection space whereviscous medium transported by the gaseous flow is collected. Then,collected viscous medium can be collected from the collection space forreuse. Preferably, the collection space, or waste storage, is locatedbefore the filter, as seen in the direction of the gaseous flow.

[0049] The jetting device having the features of the present inventionis preferably comprised in an assembly. Then, the flow generator ispreferably located away from the jetting assembly, communicating withthe assembly through a gas or pneumatic interface, which in turncommunicate with the inlet through a guide, i.e. channels, provided inthe assembly.

[0050] Further objects and advantages of the present invention will bediscussed below by means of exemplifying embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Preferred embodiments of the invention will be described belowwith reference to the accompanying drawings, in which:

[0052]FIG. 1 is a perspective view showing the general outline of amachine for application of solder paste comprising a jetting deviceaccording to the present invention;

[0053]FIG. 2 is a schematic view from above of an embodiment of adocking device and a jetting assembly of the present invention;

[0054]FIG. 3 is a schematic view showing the underside of the assemblyshown in FIG. 2;

[0055]FIG. 4 is a sectional view of a first embodiment of the centralportion of an assembly comprising a jetting device according to oneembodiment of the present invention;

[0056]FIG. 5a is an alternative sectional view of the embodiment shownin FIG. 4, and FIGS. 5b and 5 c are enlarged sectional views showing aportion thereof in greater detail;

[0057]FIG. 6a is a similar view as FIG. 5a illustrating an alternativeembodiment of the central portion of the assembly, and FIG. 6b is anenlarged sectional view showing a portion thereof in greater detail; and

[0058]FIG. 7 is an enlarged sectional view of an alternative embodimentof the device according to the invention.

DETAILED DECRIPTION OF EXEMPLIFYING EMBODIMENTS

[0059]FIG. 1 illustrates the general outline of a preferred embodimentof a machine 1 for providing a substrate 2 with deposits by dispensingdroplets of a viscous medium onto the substrate 2, i.e. jetting, inaccordance with the present invention. For ease of description, theviscous medium will hereinafter be referred to as solder paste, which isone of the alternatives defined above. For the same reason, thesubstrate will be referred to as an electric circuit board and the gaswill be referred to as air. In this embodiment, the jetting machine 1 isof a type comprising an X-beam 3 and an X-wagon 4, which is connected tothe X-beam 3 via an X-rail 16 and reciprocatingly movable along theX-rail 16. The X-beam, in turn, is reciprocatingly movably connected toa Y-rail 17, the X-beam 3 thereby being movable perpendicularly to theX-rail 16. The Y-rail 17 is rigidly mounted in the jetting machine 1.Generally, the movements are provided by linear motors (not shown).

[0060] Furthermore, the jetting machine 1 comprises a conveyor 18 forcarrying the board 2 through the jetting machine 1, and a locking device19 for locking the board 2 when jetting is to take place.

[0061] A docking device 8 is connected to the X-wagon 4 for enablingreleasable mounting of an assembly 5 at the docking device 8. Theassembly 5 is arranged for dispensing droplets of solder paste, i.e.jetting, which impact and form deposits on the board 2. The jettingmachine 1 also comprises a vision device 7, which in this embodiment isa camera. The camera 7 is used for determining the position and rotationof the board 2 and for checking the result of the dispensing process byviewing the deposits on the board 2.

[0062] Additionally, the jetting machine 1 comprises a vacuum ejector 6arranged on the X-wagon 4, and a source of compressed air (not shown).The vacuum ejector 6, as well as the source of compressed air, is incommunication with the docking device 8 via an air conduit interfacewhich are connectable to a complementary air conduit interface, in thisembodiment indicated as input nipples 9, see FIG. 2, of the dockingdevice 8.

[0063] As understood by those skilled in the art, the jetting machinecomprises a control unit (not explicitly shown) for executing softwarerunning the machine.

[0064] Briefly, the jetting machine works as follows. The board 2 is fedinto the jetting machine 1 by means of the conveyor 18, upon which theboard 2 is placed. When the board 2 is in the correct position under theX-wagon 4, the board 2 is fixed with the aid of the locking device 19.By means of the camera 7, fiducial markers are located, which markersare prearranged on the surface of the board 2 and used to determine theprecise position thereof. Then, by moving the X-wagon over the board 2in a predetermined (pre-programmed) pattern and operating the jettingassembly 5 at predetermined locations, solder paste is applied on theboard 2 at the desired locations.

[0065] With reference to FIGS. 2-3, a preferred embodiment of thejetting assembly 5, in accordance with the present invention, will nowbe described in more detail. The jetting assembly comprises an assemblyholder 11 for connecting the jetting assembly 5 to an assembly support10 of the docking device, see FIG. 2. Further, in this embodiment thejetting assembly 5 comprises a supply container 12 providing a supply ofsolder paste, and an assembly housing 15. The jetting assembly 5 isconnected to the vacuum ejector 6 and the source of pressurised air viaa pneumatic interface comprising inlets 42, positioned to interface inairtight engagement with a complementary pneumatic interface comprisingoutlets 41, of the docking device 10.

[0066] With reference now to FIGS. 4-7, the contents and function of thedevice enclosed in the assembly housing will be explained in greaterdetail. As can be seen in these sectional views, the jetting assembly 5includes a jetting device comprising an actuator locking screw 20 forsupporting an actuator in the assembly housing 15, and a piezoelectricactuator 21 formed by a number of thin, piezoelectric elements stackedtogether to form an actuator 21, which is rigidly connected to thelocking screw 20. The jetting device further comprises a bushing 25rigidly connected to the assembly housing 15, and a plunger 23 rigidlyconnected to the end of the piezoelectric actuator 21, opposite theposition of the locking screw 20. The plunger 23 is axially movablewhile slidably extending through a bore in the bushing 25. Cup springs24 are provided to resiliently balance the plunger 23 against theassembly housing 15, and for providing a preload for the actuator 21. Aneject control unit (not shown) applies a drive voltage intermittently tothe piezoelectric actuator 21, thereby causing an intermittent extensionthereof and hence a reciprocating movement of the plunger with respectto the assembly housing 15, in accordance with solder pattern printingdata.

[0067] Further, the jetting device comprises an eject nozzle 26operatively directed against the board 2, onto which small droplets ofsolder paste are to be jetted. In the nozzle 26, there is comprised ajetting orifice 27 through which the droplets are jetted. The surfacesof the nozzle 26 surrounding the jetting orifice 27 and facing thesubstrate 2 will be referred to as a jetting outlet. The plunger 23comprises a piston portion which is slidably and axially movablyextending through a piston bore 35, an end surface of said pistonportion of the plunger 23 being arranged close to said nozzle 26. Aneject chamber 28 is defined by the shape of the end surface of saidplunger 23, the inner diameter of the bushing 25 and the nozzle orifice27. Axial movement of the plunger 23 towards the nozzle 26, saidmovement being caused by the intermittent extension of the piezoelectricactuator 21, will cause a rapid decrease in the volume of the ejectchamber 28 and thus a rapid pressurization and jetting through thenozzle orifice 27, of any solder paste contained in the eject chamber28.

[0068] Solder paste is supplied to the chamber from the supply container12, see FIG. 2, via a feeding device. The feeding device comprises anelectric motor (not shown) having a motor shaft 29 partly provided in atubular bore 30, which extends through the assembly housing 15 to anoutlet 36 communicating via a tubular bore 31 with said piston bore 35.An end portion of the motor shaft 29 forms a rotatable feed screw 32which is provided in, and coaxial with, the tubular bore 30. Anessential portion of the rotatable feed screw 32 is surrounded by anarray of resilient, elastomeric o-rings 33 arranged coaxially therewithin the tubular bore 30, the threads of the rotatable feed screw 32making sliding contact with the innermost surface of the o-rings 33.

[0069] The pressurized air obtained from the above-mentioned source ofpressurized air (not shown) is arranged to apply a pressure on thesolder paste contained in the supply container 12, thereby feeding saidsolder paste to an inlet port 34 communicating with the tubular bore 30.An electronic control signal provided by a supply control unit (notshown) to the motor causes the motor shaft 29, and thus the rotatablefeed screw 32, to rotate a desired angle, or at a desired rotationalspeed. Solder paste captured between the threads of the rotatable feedscrew 32 and the inner surface of the o-rings 33 are then made to travelfrom the inlet port 34 to the piston bore 35 via the outlet port 36 andthe tubular bore 31, in accordance with the rotational movement of themotor shaft 29. A sealing o-ring 22 is provided at the top of the pistonbore 35 and the bushing 25, such that any solder paste fed towards thepiston bore 35 is prevented from escaping from the piston bore 35 andpossibly disturbing the action of the plunger 23.

[0070] The solder paste is then fed into the eject chamber 28 from anoutlet port 36 of the tubular bore 30 via the conduit 31 and a channel37. The channel 37 is provided in the piston portion of the plunger 23,wherein said channel 37 has a first portion extending axially into saidplunger and communicating with the conduit 31, and a second portionextending coaxially with and within said plunger 23 from said firstportion to the end surface of the plunger facing the eject chamber 28.

[0071] Turning now to the FIGS. 4-5c, there will be described a specificpreferred embodiment of the present invention. As can most clearly beseen in FIG. 5b, the jetting device of the jetting assembly 5 comprisesa support plate 14 located below or downstream of the nozzle orifice 27,as seen in the jetting direction. The support plate 14 is provided witha through hole 13, through which the jetted droplets may pass withoutbeing hindered or negatively affected by the support plate 14.Consequently, the hole 13 is concentric with the nozzle orifice 27.

[0072] According to this embodiment, the jetting assembly 5 comprises anair flow chamber 38 consisting of a first portion defined by the nozzleorifice 27, the nozzle 26 and the support plate 14, said first portiondefining a disc shaped space concentric with the piston bore 35; asecond portion defined by the nozzle 26 and the support plate 14,connected to said first portion and extending coaxially about the nozzle26; and a third portion defined by the assembly housing 15 and thebushing 25, connected to the second portion, parallel with the pistonbore 35 and extending coaxially around the part of the bushing 25 facingsaid third portion.

[0073] The air flow chamber 38 communicates with an air flow conduit 39located on the side of the piston bore 35 opposite that of the tubularbore 31. The air flow conduit 39 comprises a first portion extendingfrom the third portion of the air flow chamber 38 to a second portion ofthe air flow conduit, said first portion being parallel with the pistonbore 35. Said second portion is in the form of a bore that is alignedwith the conduit 31, and is arranged to provide a channel between theair flow chamber and a waste container 50 described below.

[0074] Connected to the jetting assembly 5 is a releasably mounted wastecontainer 50, for collecting of fragments of solder paste. The wastecontainer 50 can be best seen in FIG. 5a, where it is shown in itsentirety. The waste container 50 is connected to the jetting assembly 5at an interface on the jetting assembly 5, via a corresponding interfacearranged on said waste container 50. The waste container 50, which willbe described in more detail below, provides an interface andcommunication between the jetting assembly 5 and the vacuum ejector 6.Thereby, the negative pressure or vacuum produced by the vacuum ejectoris conveyed to the jetting assembly 5, and to the communicating air flowconduit 39 and airflow chamber 38.

[0075] The waste container 50 comprises an air conduit 53, having afirst portion communicating with said connecting interface and beingaligned with the air flow conduit 39 of the jetting assembly, and asecond portion extending perpendicularly from said first portion. Theair conduit 53 communicates with a collection space 55 over a separatingwall 54, the collection space being arranged for collection of solderpaste residue removed from the jetting outlet.

[0076] At the top of the collection chamber 55, a narrow air conduit 52leads the air flow from the collection chamber 55 into a filter 57. Thefilter 57 is of conventional type and provided for preventing anyfragments of solder paste not collected in the collection chamber 55from reaching the vacuum ejector. The filter is further provided in alongitudinal bore 56 and is in communication with an outlet conduit 58.

[0077] The waste container 50 is releasably connected to a vacuumejector 6, of conventional type, for evacuating the waste container 50.The vacuum ejector 6 is connected to the waste container 50 via the airoutlet 58, a connector 60 and an air tube 61. Even though the vacuumejector is illustrated as being separate from the jetting assembly 5and/or the waste container 50, a number of other placements orcombinations of the vacuum ejector 6, the jetting assembly 5, and thewaste container 50 are of course conceivable within the scope of thepresent invention.

[0078] In operation, the vacuum ejector evacuates the waste container,including evacuation of the collection space 55 the narrow air conduit52, the longitudinal bore 56 and the filter 57, the outlet conduit 58,the connector 60 and the air tube 61. This evacuation produces an airflow through the waste container as indicated by the arrows in FIG. 5a.As a consequence, air flow conduit 38 and air flow chamber 39 of thejetting assembly 5 are also evacuated via the interface. Thus, air issucked in through the outlet hole 13, which gives rise to a strong airflow in a direction reverse to that of the jetted droplets. This airflow will pass the jetting outlet and remove any undesired residue ofsolder paste that may have become adhered to the jetting outlet, forreasons described above.

[0079] According to the present embodiment of the invention, the airflow is provided before, during and after the jetting of each droplet.Also, the air flow could also be provided intermittently, following apredetermined time period of jetting, or following a predeterminednumber of jetted droplets. It is also contemplated that the accumulationor build-up of solder paste residue at the jetting outlet is monitored,and that the flow of air is provided when the accumulation reaches acertain level. However, it is preferred that the air flow is constantlyprovided during the jetting process.

[0080] The air will flow through the air flow chamber 38 and continueinto the waste container 50 via the air flow conduit 39. Due to theforce of the air flow, solder paste fragments removed from the vicinityof the jetting outlet will be transported or carried through the airflow chamber 38, the air flow conduit 39 and into the waste container50. Inside the waste container 50, the air will flow through the airconduit 53, over the separating wall 54 and into the collection chamber55. Due to the force of gravity, the majority of the solder pasteresidue transported by the air flow will fall into the collectionchamber 55, while the air flow will continue into the narrow conduit 52.Any residue of solder paste that may continue along with the air flowinto the narrow conduit 52, will be collected by the filter 57, thuspreventing fragments of solder paste from reaching the outlet conduit58.

[0081] Furthermore, as the jetted droplets face a strong head windimmediately following the jetting thereof, and droplets having a jettingtrajectory with an angular deviation from that intended, will encountera slight side wind. The effect of the side wind on a jetted droplet willbe dependent of the magnitude of angular deviation. As a consequence,the angular deviation can be enhanced to such an extent that the jetteddroplet will “miss” the hole 13 and instead be collected by the supportplate 14. The above may also be the case for any satellites, describedabove, which due to their angular deviation will encounter a side windand be collected by the support plate 14. Then, the air flow present orlater produced in the air flow chamber will transport away any solderpaste collected by the support plate 14. Due to the lower velocity andsignificantly smaller volume of the satellites, as compared to thesolder paste droplets, the satellites will be much more prone to beaffected by the side wind.

[0082] According to an alternative embodiment of the invention, thesupport plate 14 comprises one or more additional holes. Then, the hole13 arranged coaxially with the nozzle 27 is primarily used for providinga path for jetted droplets, while the other hole(s) are used forproviding an inlet of air into the air flow chamber 39. Naturally, thepositioning and design of the other hole(s) must be such that a forcefulflow of air is provided at or past the jetting outlet.

[0083] According to FIG. 7, an alternative embodiment of a support plate114 is illustrated. In this embodiment, the wall of the support plate114 is adjacent the hole 113 directed at an angle towards the jettingoutlet. The illustrated design of the support plate 114 will provide acontraction in the flow path for the air flow, which will increase thevelocity of the air flow immediately adjacent the jetting outlet.Furthermore, according to this embodiment, the inward surface of theorifice, i.e. the surface facing the viscous medium droplet as thedroplet passes the orifice, is very small. This reduces the risk ofviscous medium attaching to the wall surface.

[0084] As realized by the man skilled in the art, a multitude ofalternative designs for narrowing the flow path at or past the jettingoutlet are conceivable without departing from the scope of the presentinvention.

[0085] With reference now to FIGS. 6a and 6 b, there is illustrated analternative embodiment of a device according to the present invention.Since the general function of the jetting device is the same asdescribed above, it will not be described further. According to thepresent embodiment, a waste container 50 and a vacuum ejector 6 ismounted to the jetting assembly 5, preferably releasably mounted.However, there is no interface between the waste container 50 and thejetting assembly 5. Instead, the air conduit 53 of the waste container50 extends to the vicinity of the nozzle 26 and nozzle 27. The remainderof the waste container as well as the vacuum ejector are no differentfrom that described above, and will therefore not be discussed further.

[0086] As described above, a source of pressurized air is connected tothe jetting assembly 5 via a pneumatic interface, the main task for thepressurized air being described above. According to this specificembodiment, the pressurized air is also used for providing a flow ofpressurized air at the jetting outlet. This is achieved by directing aflow of pressurized air from the source, through a guide (not shown),i.e. air conduits or channels, to a pressurized air outlet 40 extendingto and being directed against the nozzle 27 and the jetting outletthereof.

[0087] As can be seen in FIGS. 6a and 6 b, the outlet of pressurized air40 is located opposite the inlet 53 of the waste container 50. Thus, theblowing effect provided by the pressurized air is combined with thesuction effect of the vacuum ejector 6, which will transport undesiredresidue of solder paste from the jetting outlet. Consequently, therewill be a strong air flow across and intersecting the path of the jetteddroplets, which air flow will transport undesired residue of solderpaste from the jetting outlet.

[0088] Even though the present embodiment has been illustrated without asupport plate, the inclusion of such a plate in this embodiment is ofcourse conceivable within the scope of the invention. Then, the flow ofair, as indicated by arrows in FIG. 6b, will be present in a chamber orspace defined between such a support plate and the nozzle 27.

[0089] The magnitude of the air flow force will have to be controlledsuch that no adverse effects on the jetting trajectory of the jetteddroplets results from the air flow. However, a constant minor deviationin a given direction can be compensated for by adjusting the position ofthe jetting assembly, i.e. the nozzle, when jetting.

[0090] Even though the present invention has been described above usingexemplifying embodiments thereof, alterations, modifications, andcombinations thereof, as understood by those skilled in the art, may bemade without departing from the scope of the invention, which is definedin the accompanying claims. For example, the invention is not restrictedto the use of a jetting assembly. On the contrary, the device and methodof the present invention in a machine for jetting viscous medium withouta jetting assembly are readily realized and comprised within the scopeof the invention.

1. A method of jetting droplets of viscous medium onto a substrate, saidjetting device comprising a jetting outlet through which said dropletsare jetted, comprising the steps of providing a gaseous flow past thejetting outlet such that an adverse effect on the performance of thejetting device that may result from accumulation of viscous mediumresidue at the jetting outlet is prevented, providing a wall at thejetting outlet, said wall being located downstream of the jetting outletseen in the jetting direction, and providing an orifice in said wall forpermitting the jetted droplets to pass through the orifice, the orificeand the jetting outlet being aligned in the jetting direction:
 2. Themethod according to claim 1, comprising the step of providing theorifice with such dimensions that undesired viscous medium satellites,produced during the jetting of droplets, that deviate from the generaldirection of the jetted droplets are collected by said wall.
 3. Themethod according to claim 2, wherein said gaseous flow is provided suchthat viscous medium collected by said wall is removed from said wall bysaid gaseous flow.
 4. The method according to claim 1, comprising thestep of providing a path for the gaseous flow past the jetting outletbetween said wall and said jetting outlet.
 5. The method according toclaim 1, comprising the step of designing said wall so that the gaseousflow adjacent the jetting outlet is focused and the velocity of thegaseous flow is increased past the jetting outlet.
 6. The methodaccording to claim 4 or 5, wherein said gaseous flow is provided throughsaid orifice, towards the jetting outlet, and away from the jettingoutlet in a radial direction along the path provided between said walland jetting outlet.
 7. The method according to claim 6, wherein saidgaseous flow is provided such that a stabilizing effect on the jettingtrajectory of the jetted droplets is obtained.
 8. The method accordingto claim 1, wherein the gaseous flow at the jetting outlet is directedalong a flow path that intersects the jetting path of the jetteddroplets.
 9. The method according to claim 8, wherein said gaseous flowsweeps along the jetting outlet.
 10. The method according to claim 8 or9, wherein said flow path is essentially perpendicular to said jettingpath at the jetting outlet.
 11. A method of jetting droplets of viscousmedium onto a substrate, said jetting device comprising a jetting outletthrough which said droplets are jetted, comprising the step of providinga gaseous flow past the jetting outlet such that an adverse effect onthe performance of the jetting device that may result from accumulationof viscous medium residue at the jetting outlet is prevented, whereinthe gaseous flow at the jetting outlet is directed along a flow paththat intersects the jetting path of the jetted droplets.
 12. The methodaccording to claim 11, wherein said gaseous flow sweeps along thejetting outlet.
 13. The method according to claim 11 or 12, wherein saidflow path is essentially perpendicular to said jetting path at thejetting outlet.
 14. The method according to claim 1, wherein the gaseousflow is provided such that viscous medium residue is removed from thejetting outlet.
 15. The method according to claim 1, wherein saidgaseous flow is provided following the jetting of a series of jetteddroplets.
 16. The method according to claim 1, wherein said gaseous flowis provided following a predetermined number of jetted droplets.
 17. Themethod according to claim 1, wherein said gaseous flow is providedfollowing a predetermined time period during which droplets have beenjetted.
 18. The method according to claim 1, wherein said gaseous flowis provided such that the jetting outlet is kept free of viscous mediumresidue.
 19. The method according to claim 18, wherein said gaseous flowis provided during the jetting of said droplets.
 20. The methodaccording to claim 1, wherein the gaseous flow is continuously providedduring, between and following the jetting of droplets.
 21. The methodaccording to claim 1, wherein said gaseous flow is provided such thatthe presence of undesired viscous medium satellites produced during thejetting of droplets is reduced, said satellites being transported awayby the gaseous flow.
 22. The method according to claim 1, comprising thestep of directing and focusing the gaseous flow adjacent the jettingoutlet such that the velocity of the gaseous flow is increased past thejetting outlet.
 23. The method according to claim 1, comprising the stepof directing and focusing the gaseous flow adjacent the jetting outletsuch that the ability of the gaseous flow to transport viscous mediumresidue from the jetting outlet is increased.
 24. The method accordingto claim 1, comprising the step of providing a suction generator forproviding said gaseous flow.
 25. The method according to claim 1,comprising the step of providing a blow generator for providing saidgaseous flow.
 26. The method according to claim 1, comprising the stepof providing a suction generator and a blow generator in combination forproviding said gaseous flow.
 27. The method according to claim 1,comprising the steps of directing said gaseous flow after having passedthe jetting outlet into a viscous medium waste compartment, andcollecting in said waste compartment viscous medium transported from thejetting outlet by the gaseous flow.
 28. The method according to claim 1,comprising the steps of directing said gaseous flow through a filterafter said gaseous flow have passed the jetting outlet, and collectingby said filter viscous medium transported from the jetting outlet by thegaseous flow.
 29. The method according to claim 1, wherein the gas usedfor providing said gaseous flow is air.
 30. The method according toclaim 1, wherein the gas used for providing said gaseous flow isnitrogen.
 31. A method of jetting droplets of viscous medium onto asubstrate, said jetting device comprising a jetting outlet through whichsaid droplets are jetted, comprising the step of providing an air flowpast the jetting outlet such that an adverse effect on the performanceof the jetting device that may result from accumulation of viscousmedium residue at the jetting outlet is prevented, wherein said air flowis provided through suction during, between and following the jetting ofindividual droplets.
 32. A device for jetting droplets of viscous mediumonto a substrate, said device comprising a nozzle having a jettingoutlet through which said droplets are jetted, a flow generator forproducing a gaseous flow, a flow guide for providing a flow path forsaid gaseous flow past the jetting outlet, such that an adverse effecton the performance of the jetting device that may result fromaccumulation of viscous medium residue at the jetting outlet isprevented, wherein said flow guide comprises a wall located at thejetting outlet, said wall being located downstream of the jetting outletseen in the jetting direction, said wall and said nozzle defining afirst space there-between, and a first orifice provided in said wall,said first orifice and the jetting outlet being aligned along the pathof the jetted droplets, said first orifice being designed to permitjetted droplets to pass through said first orifice essentiallyunaffected, wherein said flow guide is arranged to provide said gaseousflow within said first space along a flow path past the jetting outlet.33. The device according to claim 32, wherein said wall and said jettingoutlet are formed as one integral structure.
 34. The device according toclaim 32, wherein said first space is provided with an inlet and anoutlet for said gaseous flow.
 35. The device according to claim 34,wherein said inlet and said outlet are provided on opposite sides of thejetting outlet, such that said gaseous flow intersects the path of thejetted droplets.
 36. The device according to claim 35, comprising a blowgenerator communicating with said inlet.
 37. The device according toclaim 34, wherein said first orifice constitutes said inlet for saidgaseous flow into said first space.
 38. The device according to claim34, further comprising at least one second orifice in said wall, saidsecond orifice constituting said inlet for said gaseous flow into saidfirst space.
 39. The device according to claim 34, wherein said flowguide comprises at least one channel running within said wall forproviding a flow path within said wall for said gaseous flow.
 40. Thedevice according to claim 39, wherein said at least one channel isprovided with at least one opening towards said first space at thejetting outlet, said opening constituting said inlet for said gaseousflow into said first space.
 41. The device according to claim 40,wherein said at least one opening is directed at the jetting outlet. 42.The device according to claim 32, wherein the dimensions of said firstorifice are such that jetted droplets are permitted to pass through saidfirst orifice, while viscous medium satellites, produced during thejetting of droplets, that deviate from the general direction of thejetted droplets are collected by said wall.
 43. The device according toclaim 32, wherein said wall is arranged to narrow the flow path for thegaseous flow at the jetting outlet such that the flow velocity past thejetting outlet is increased.
 44. The device according to claim 32,wherein said wall is arranged to narrow the flow path for the gaseousflow at the jetting outlet, such that the gaseous flow has an increasedability to transport viscous medium residue from the vicinity of thejetting outlet.
 45. The device according to claim 43 or 44, wherein saidwall is provided with at least one protrusion at said first orifice,said protrusion being directed towards the jetting outlet for providingsaid narrowed flow path.
 46. The device according to claim 32, whereinthe surface of the wall facing the substrate and surrounding the firstorifice is bevelled.
 47. A device for jetting droplets of viscous mediumonto a substrate, said device comprising a nozzle having a jettingoutlet through which said droplets are jetted, a flow generator forproducing a gaseous flow, a flow guide for providing a flow path forsaid gaseous flow past the jetting outlet such that an adverse effect onthe performance of the jetting device that may result from accumulationof viscous medium residue at the jetting outlet is prevented, said flowguide being arranged for providing said flow path in a direction thatintersects the jetting path of the jetted droplets.
 48. The deviceaccording to claim 47, wherein said flow guide is arranged for directingsaid gaseous flow along the jetting outlet.
 49. The device according toclaim 47 or 48, wherein said flow guide is arranged for directing saidgaseous flow essentially perpendicular to said jetting path at thejetting outlet.
 50. The device according to claim 32, comprising afilter arranged downstream of said jetting outlet as seen in thedirection of said gaseous flow, said filter being arranged to collectviscous medium transported by said gaseous flow.
 51. The deviceaccording to claim 32, comprising a collection space arranged downstreamof said jetting outlet as seen in the direction of said gaseous flow,said collection space being arranged for collecting viscous mediumtransported by said gaseous flow.
 52. The device according to claim 32,wherein said flow generator comprises a blow generator, and wherein saidflow guide is arranged for providing a flow path from said blowgenerator and past the jetting outlet.
 53. The device according to claim32, wherein said flow generator comprises a suction generator, andwherein said second flow guide is arranged for providing a flow pathbetween the jetting outlet and said suction generator.
 54. The deviceaccording to claim 32, wherein said flow generator comprises a suctiongenerator and a blow generator, wherein said flow guide is arranged forproviding a flow path between said blow generator and the jettingoutlet, and between the jetting outlet and said suction generator. 55.The device according to claim 32, wherein the gas used for keeping thenozzle free of viscous medium residue is air.
 56. The device accordingto claim 32, wherein the gas used for keeping the nozzle free of viscousmedium due is nitrogen.